From DE 24 36 230 A1 an optical system is known for the rotation of images in a recording lens system for television cameras, movie film cameras and photographic cameras. The optical system contains a prism which serves for the rotation of the image and which is mounted between a forward lens and a rear lens of a relay-lens system, as well as a field lens which is mounted on a first focusing plane on which an image is created through an objective lens. The field lens has a focal distance such that the pupil of the relay-lens system conjugated to the opening of the objective lens can be arranged in the centre point of the beam path of the prism which is serving for the rotation of the image.
From DE 3245 477 A1 an optical system is known for image rotation which has a projection lens system for creating an image in a predetermined plane, a prism for image rotation rotatable about the optical axis of the projection lens system, and a slit element for screening light which is mounted between the projection lens system and the prism and which is rotatable with the rotation of the prism about the optical axis.
The use of an optical system of this kind for image rotation in conjunction with a film camera means that when an image rotation is required it is no longer necessary to rotate the entire film camera about the optical axis so that the film camera can be operated as normal and the eyepiece as well as all operating elements of the film camera remain in their standard position. The use of standard lenses and standard accessories is thereby guaranteed and these can be fitted on hand-held systems or on systems fixed to the body of the cameraman.
From U.S. Pat. No. 4,427,269 a method and device are known for automatically compensating the image rotation through an articulated optical system which consists of members with lenses for the optical representation as well as articulated joints with mirrors or prisms for deflecting the beam path. In order to compensate the image rotation when the articulated optical system rotates a signal is generated whose polarity is dependent on the direction of rotation of the image produced in an observation plane relative to an object. From this signal a compensation element mounted in the beam path of the articulated optical system is controlled and actuated until the signal disappears. The compensation element consists of an optical element for image rotation formed as a Dove prism and mounted inside one tube of the several interconnected tubes of the articulated optical system and connected through gearing to a motor mounted outside of the tube and controlled by a servo booster.
The servo booster receives a signal from a signal processor which is connected to a sensor mounted on the observation plane and on which an image is depicted of markings arranged inside or outside an intermediate image. If this marking deviates from a predetermined neutral position then the sensor produces a signal which leads through the signal processor and the servo booster to control the motor which through the gearing turns the optical element for compensating the image rotation until the image marking is again located in the neutral position.
From U.S. Pat. No. 5,677,763 an optical measuring and viewing device is known with which physical and optical characteristics of an object are measured by means of a device for image rotation which can consist of a Dove prism, a Pechan prism or a mirror assembly and the measured beams are sent to a one-dimensional CCD element. The image-rotating optical element is mounted inside a tube which is supported through ball bearings on a housing on which a drive motor is fixed which is connected through a drive belt to the image-rotating optical element. Additional optical elements such as planar concave lenses, aperture and a planar convex lens are mounted outside of the tube but inside the housing of the optical measuring and viewing device and are fixedly connected to same.
The aforementioned U.S. Pat. No. 4,427,269 and U.S. Pat. No. 5,677,763 specification are directed more particularly to the needs for compensating image rotations in an articulated optical system and for measuring the outlines of an object. The demands on an optical system for rotating recorded images of a film camera differ quite considerably from this.
One requirement of an optical system of a film camera is the light intensity of the optical system used, for only with an optical system having a high light intensity can satisfactory film shots be produced even with high-speed films and under unfavourable lighting conditions. A further requirement for an optical system of a film camera lies in its simple handling which is also to include minimal size and easy assembly and dismantling. Furthermore in order to produce special effects when filming, extremely high dynamics of the optical system have to be guaranteed so that inter alia the so-called “stroboscopic effects” can be achieved, i.e. special effects which are connected with a sudden change of the position of the horizon line. Extremely high dynamics of this kind require special mechanical measures in order to keep the moved masses slight and to ensure a direct force or torque transfer.